1. Field of the Invention
The present invention relates to generally to ram air parachutes and more particularly to a design of a canopy of a ram air parachute.
2. Discussion of Related Art
Parachutes have evolved over the years into highly sophisticated systems, and often include features that improve the safety, maneuverability, and overall reliability of the parachutes. Initially, parachutes included a round canopy. A parachute harness skydiver was connected to the canopy by suspension lines disposed around the periphery of the canopy. Such parachutes severely lacked control. The user was driven about by winds without any mechanism for altering direction. Furthermore, such parachutes had a single descent rate based upon the size of the canopy and the weight of the parachutist.
In the mid-1960""s the parasol canopy was invented. Since then, variations of the parasol canopy have replaced round canopies for most applications, particularly for aeronautics and the sport industry. The parasol canopy, also known as a ram air canopy, is formed of two layers of materialxe2x80x94a top skin and a bottom skin. The skins may have different shapes but are commonly rectangular or elliptical. The two layers are separated by vertical ribs to form cells. The top and bottom skins are separated at the lower front of the canopy to form inlets. During descent, air enters the cells of the canopy through the inlets. The vertical ribs are shaped to maintain the canopy in the form of an airfoil when filled with air. Suspension lines are attached along at least some of the ribs to maintain the orientation of the canopy relative to the ground. The canopy of the ram air parachute functions a wing to provide lift and forward motion. Guidelines operated by the user allow deformation of the canopy to control direction and speed. Ram air parachutes have a high degree of maneuverability.
Canopies are flexible and stretchable membrane structures, they distort based upon mechanical and aerodynamic tensions, stresses, airflows and pressure distribution. Although a cell is modeled as having a basically rectangular cross section, when inflated the shape distorts towards round with complex distortions. Under canopies of conventional design, the leading edge or nose of the ram air parachute is deformed during flight. With forward motion, the head-on wind overcomes the internal pressurization of the canopy, and deforms the nose of the canopy. This distortion blunts the nose of the airfoil or even indents it, and impairs the aerodynamics of the parachute wing. The parachute flies less efficiently as a result. Therefore, a need exists for a ram air parachute canopy which reduces deformations of the nose.
Para-gliders and powered parachutes, which operate with similar designs to ram air parachute canopies, overcome the deformation problem by including xe2x80x9cstiffenersxe2x80x9d in the nose of the canopy. Typically, the stiffeners are plastic or mylar sheets sewn on the vertical ribs of the canopy into the nose. The stiffeners reinforce the nose of the canopy and help maintain its shape. The stiffeners also function to keep open the inlets of the canopy when not inflated to aid in the launching of para-gliders and powered parachutes. However, the stiff plastic or mylar used in paragliders and powered parachutes is not applicable to skydiving or other freefall deployable parachutes. A deployable system must be packed into a small space and must open efficiently. The stiffeners cannot be compressed as required for packing the parachute. When stiffeners become crushed, they remain creased or bent and create additional deformation of the nose of the canopy, which hinders proper operation of the parachute. Packing for free fall deployment of such para-glider or powered parachute is not possible due to the stiffeners.
Accordingly, there exists a need for a stiffener for use on a parachute to reduce nose-deformation to improve the canopy""s aerodynamics, which may be folded and packed as known in the art of deployable parachutes.
The deficiencies of prior art ram air parachutes are substantially overcome by the present invention which provides flexible stiffeners to prevent deformation of the nose of the canopy during flight. According to one aspect of the invention, the flexible stiffeners are wire rings that act as springs to reinforce the nose. The ring springs are formed from a super-elastic metal alloy, i.e. nickel titanium such that they can be greatly deformed during packing and recover without kinking. Such Nixe2x80x94Ti alloys are over 8 times more deformable than spring steel. The stiffeners may be ring shaped or heat memorized into a formed shape i.e. a D shape during manufacture. Additionally the stiffeners may be attached to the vertical ribs by various methods but preferably by sewing a pocket in the section of the nose to be reinforced and inserting the stiffener ring spring. Additionally the pocket can pre-stress the ring spring into a different shape that it is at rest. I.e. from a round ring to a D shape to exactly match the leading edge of the airfoil. This has the added benefit of biasing the spring in the direction of the head on wind that acts to deform the airfoil.